President Obama, who has long sought closer relations with Iran, has reached a deal to limit Iranian nuclear plans that would once have been considered unthinkable. “It’s a major seismic shift in the region,” one expert said. “It rearranges the entire chess board.” It now seems conceivable that Iran could have a role in coming Syrian peace talks.

If the United States continues to become more engaged with Iran, how would that affect American relations with regional allies, like Saudi Arabia, a major opponent of Iran?